1. Field of the Invention
The present invention relates generally to computer-controlled image projectors and specifically to interaction between an operator and the computer-controlled image being projected, as well as a means for automatically adjusting alignment of beams in a multi-beam projector.
2. Discussion of Prior Art
A wide variety of devices have been produced for permitting an operator to manually interact with a computer and imagery produced therefrom. Such devices includes the "mouse", a "track ball", a joystick, a touch screen and an electronic chalkboard.
The "mouse" is a device in which a ball is rolled over a surface and the amount of roll is sensed and governs the incremental movement of a computer generated position indicator, such as a cursor on the screen from an initial point on the image to some desired destination point. In order to accommodate slippage or sticking between the ball and the surface, there is generally no fixed relationship between the orientation of the ball and any image point. Efficient operation requires a certain amount of practice and/or training by the operator.
Similarly, the "track ball" is mounted for rotation in a fixed position and the ball is rotated by the operator's hand or fingers with the same general effect as the mouse, i.e. movement of a computer-generated position indicator.
A joystick, as in an airplane control device, is a control stick that can be tilted in two axes. Although the tilt angle may be directly related to the image location, precision of the operation is difficult to achieve. Alternatively, in some embodiments, the tilt angle is used to establish the rate of movement with the tilt direction indicative of the direction of movement of the cursor. Efficient operation of such a device is definitely a learned operation.
A light pen device is utilized with a raster-scanned cathode ray tube (CRT) wherein a light detector at the tip of the pen senses passage of the CRT electron beam, making it possible to time-relate beam passage to pen/image location. Pointing accuracy Or resolution is affected by the distance between the light pen and the phosphor layer and is degraded by faceplate thickness, glare filters, etc. While such a device is useable with projected CRT imagery, it is not useable with non-scanned and/or matrix-addressed imagery (three color projection systems, LCD projection systems, etc.).
Touch screen systems utilize a stylus which is brought into close proximity to the screen image and the location of the stylus is sensed by means of its interaction with a reference field established over the image and generated optically, magnetically, inductively or otherwise. The "reference field" requirement makes it necessary to fix the image size and ease of operation and resolution cannot be improved by enlargement of the image.
The electronic chalkboard is a device like a blackboard or a writing tablet which can be written upon and the writing can be sensed in some fashion as with a touch screen for later storage and printout. Unlike a touch screen, erasure and correction becomes somewhat complicated. Like a touch screen, cost and complexity tend to be strongly affected by image size.
The difficulty with all of the above devices is that they are generally cable connected to a computer. Although cordless versions of some are available, implementation of this feature is relatively costly and complex.
Additional difficulties with the above (except perhaps the electronic chalkboard) are that their use is not intuitive, requiring the learning and practice of unfamiliar manual techniques. Precise and tedious operation is generally required in order to operate down to the resolution of most imagery.
An additional problem exists where multi-beam projectors create a composite image, made up of overlapping images projected from two or more beam projection systems. The most common of these is the conventional three-gun projection television in which a separate gun, one for each of three primary colors, projects its respective image on a screen. The three images when properly aligned with one another create a composite color image. Unfortunately, if the distance between the projector and the screen changes, the coincidence of three images will also change leading to an unfocused image appearance.
Furthermore, even without changing the distance between the projector and the viewing screen, temperature changes and other environmental effects can cause the three-gun projection system to go out of adjustment resulting in misaligned images and a deteriorated image quality.